A selectable one way clutch (OWC) to be used in automatic transmissions replaces the friction discs OWC actuated by oil pressure with a strut-based selectable OWC actuated by an electromagnetic module controlled by the transmission ECU. This reduces the drag losses associated with the friction disc clutch of prior designs when it is open and over-running continuously while the transmission is running and may also offer cost reductions associated with the removal of the components of the friction discs clutch (friction discs, pressure plates, end plate, piston and seals).
In one prior art embodiment of a selectable OWC for a transmission, a coil is wound around a steel magnetic pole, which when electrically energized, acts to close the gap (such as an air gap) between the end poles (i.e., north and south) and the one-way clutch strut end. In this design, the pole ends are magnetized, which work to attract the end portion of the strut, which is not magnetized.
In the above concept, the clutch housing does not play any role in the magnetic circuit; it only controls the relative position of the coil and struts. When an electrical charge is applied, the mechanism pulls the strut from the open position toward the closed position. The pole is magnetized and the strut is not magnetized so the housing is not part of the magnetic circuit or path.
While this arrangement is one method of actuating a strut, it requires single pole magnetic attraction which is not as robust or reliable of a lock up as might be desired depending on the application. Therefore, it is desirable in the art to provide a more robust actuation of a strut in a selectable OWC.